1. Field of the Invention
The present invention relates to a method for changing concentration of a treatment solution and a treatment solution supply apparatus.
2. Description of the Related Art
In a photolithography process in semiconductor device fabrication processes, solution treatments using treatment solutions such as a resist coating treatment of applying a resist solution to the surface of a wafer to form a resist film and a developing treatment of supplying a developing solution and a washing fluid to an exposed wafer to develop the wafer are carried out.
For example, the developing solution used in the developing treatment is conventionally stored in a large storage tank provided in a factory side with its concentration adjusted at a predetermined value following a recipe. Generally, this developing solution is supplied to a tank of a developing unit from the storage tank and temporarily stored there, and thereafter, it is supplied to a supply section for supplying the developing solution to the wafer, for example, a developing solution supply nozzle, from the tank of the developing unit when the developing treatment is carried out.
It is sometimes necessary to change the concentration of the developing solution when the recipe or the like of the wafer is changed. In this case, conventionally, the existing developing solution in the tank is completely drained out and a developing solution with a new concentration is prepared and stored again in the tank in order to change the concentration of the developing solution in the tank. Moreover, when the developing solution with the new concentration is stored, only a small volume of the developing solution left in the tank prevents strict maintenance of the concentration of the developing solution since the new developing solution and the existing developing solution are mixed together. Therefore, in changing the concentration of the developing solution, a troublesome work of once draining out the developing solution with the new concentration which is temporarily stored in the tank and storing a developing solution with the same concentration again has been carried out.
A large volume of the developing solution has to be drained out if the developing solution in the tank is thus completely drained out each time the concentration of the developing solution is changed and a large volume of the developing solution is consumed to cause cost increase. Furthermore, when the tank is large, it requires a lot of time to completely drain out the developing solution stored in this tank and thereafter, to supply the developing solution into the tank again and during that time, a wafer treatment is interrupted, which also causes a problem that a throughput is lowered.